Paul, 15 People say that motorbikes are 5 bikes because they go very fast. I don't agree. If the motorcyclist is careful, motorbikes are safe.

В пропуске необходимо употребить прилагательное fast (быстрый) в сравнительной степени. В задании дан союз than, следовательно, прилагательное употребляется в сравнительной степени.

People say that motorbikes are faster than bikes because they go very fast. I don't agree. If the motorcyclist is careful, motorbikes are safe.

Ответ: People say that motorbikes are faster than bikes because they go very fast. I don't agree. If the motorcyclist is careful, motorbikes are safe.